A semiconductor device is connected in a series circuit with battery and resistance. A current is found to pass through the circuit. When polarities of the battery are reversed the current drops to zero. The device may be:
[a] pn junction
[b]intrinsic semiconductor
[c] p type semiconductor
[d] n type semiconductor
Q.2 On increasing the reverse bias to a large value in pn junction diode the current:
[a] increases slowly [b] remains fixed
[c] suddenly increases [d] decreases slowly
Q.3 The electrical resistance of depletion layer is large because:
[a] it has no charge carriers
[b] it has large number of charge carriers
[c] it contains electrons as charge carriers
[d] it has holes as charge carriers
Q.4 To measure light intensity we use
[a] LED with forward bias
[b] LED with reverse bias
[c] photodiode with reverse bias
[d] photodiode with forward bias
Q.5 In forward biased pn junction the current is of the order of
[a] ampere [b] milliampere
[c] microampere [d] nanoampere
Q.6 When pn junction diode is reverse biased the flow of current across the junction is mainly due to
[a] diffusion of charges
[b] depends on nature of material
[c] drift of charges
[d] both drift and diffusion of charges
Q.7 In a common emitter circuit, the collector current is 0.9mA, base current is 100μA. The value of current gain and emitter current is
[a] 49 and 2mA [b] 9 ad 1mA
[c] 0.9 and 0.1mA [d] none of these
Q.8 The concentration of impurities in a transistor :
[a] equal for emitter, base and collector
[b] least for emitter region
[c] largest for emitter region
[d] largest for collector region
Q.9 Application of forward bias to the pn junction
[a] increases the number of donors on n side
[b] increases electric field in depletion region
[c] increases potential difference across the depletion region
[d]widens the depletion zone
Q.10 Within depletion region of the pn junction diode
[a] p side is positive and n side is negative
[b] p side is negative and n side is +ive
[c] both sides are either positive or negative
[d] both sides are neutral
Q.11 What is the conductivity of semiconductor if electron density= 5x1012/cm3 and hole density = 8x1013/cm3[μe=2.3 and μh=0.01 in SI units]
[a]5.634 [b] 1.968
[c]3.421 [d] 8.964
Q.12 The electrical conductivity of semiconductor increases when an electromagnetic radiation of wavelength 1125nm is incident on it. The band gap of semiconductor is
[a]0.9eV [b] 0.7eV
[c] 0.8eV [d]0.5eV
Q.13 In common base mode of transistor, the collector current is 5.488mA, the emitter current is 5.6mA. the value of current amplification factor is
[a] 48 [b] 49
[c] 50 [d] 51
Q.14 A semiconductor is doped with donor impurity is
[a] p type [b] n type
[c] npn type [d] pnp type
Q.15 IN NPN transistor, the collector current is 24mA. If 80% of the electrons reach collector, the base current in mA is
[a] 36 [b] 26
[c] 16 [d]6
Q.16 The difference in the variation of resistance with temperature in a metal and semiconductor arises essentially due to the difference in
[a] type of bonding
[b] crystal structure
[c]scattering mechanism with temperature
[d]number of charge carriers with temperature
Q.17 barrier potential of pn junction does not depend on
[a] temperature [b] forward bias
[c] reverse bias [d] diode design
Q.18 One serious drawback of semiconductors is
[a] they are costly
[b] they pollute the environment
[c] they do not last for long time
[d] they can’t withstand high voltage
Q.19 Resistance of semiconductor
[a] increases with temperature
[b] decreases with temperature
[c] remains unaffected with temperature
[d] none of these
Q.20 The dominant mechanism for motion of charge carriers in forward and reverse biased silicon pn junction are
[a] drift in both forward and reverse bias
[b]diffusion in both forward and reverse
[c] diffusion in forward and drift in reverse
[d] drift in forward and diffusion in reverse
Q.21 When NPN transistors is used as amplifier
[a] electrons move from base to emitter
[b] electrons move from emitter to base
[c] electrons move from collector to base
[d] holes move from base to emitter
Q.22 In a transistor circuit base current is increased by 50μA keeping the collector voltage fixed at 2 volts, the collector current increases by 1mA. The current gain of the transistor is
[a] 20 [b] 40
[c] 60 [d] 80
Q.23 A common emitter transistor amplifier has a current gain of 50. if the load voltage is 4kΩ and input resistance is 500Ω, the voltage gain in amplifier is
[a]160 [b] 200
[c] 300 [d] 400
Q.24 Which gate corresponds to action of parallel switches
[a] OR gate [b] AND
[c] NOR [d]NAND
Q.25 Which gate is similar to function of two series switches
[a] AND [b] OR
[c] NAND [d] NOR
Q.26 The electrical conductivity of the semiconductor increases when em radiation of wavelength shorter than 2480nm is incident on it. The band gap of the semiconductor in eV is
[a] 0.9 [b] 0.7
[c] 0.5 [d] 0.1
Q.27 If the forward voltage of semiconductor is doubled, the width of depletion layer will;
[a] become half [b] becomes 1/4th
[c] remain unchanged [d] becomes double
Q.28 A sinusoidal voltage of peak value 200V is connected to diode and resistance in series so that half wave rectification occurs. If forward resistance of the diode is negligible, the rms voltage across resistance is
[a] 200 [b] 100
[c] 100√2 [d] 283
Q.29 A common emitter amplifier is designed with npn transistor with α=0.99. the input impedance is 1 Kilo ohm and load is 10kiloohm. The voltage gain will be
[a]9.9 [b]99
[c]990 [d]9900
Q.30 The main cause of Zener breakdown is
[a]high doping [b]low doping
[c]collision ionization
[d]production of electron hole pair due to thermal excitation
Q.31 In binary number system, 11000101 represents which number on decimal system
[a] 4 [b] 401
[c] 197 [d] 204
Q.32 For common base transistor the numerical value is least for
[a] voltage gain [b] power gain
[c] resistance gain [d] current gain
Q.33 In a common emitter amplifier output resistance is 5000 ohm and input resistance is 2000 ohm. If the peak value of signal voltage is 10mV and β=50, the peak value of voltage output is
[a] 5x10-6V [b]2.5x10-4V
[c]1.25V [d]125V
Q.34 What is the value of the voltage gain in the common emitter amplifier, where input resistance is 3 ohm and load resistance is 24 ohm. Take β=0.6
[a]8.4 [b]4.8
[c]2.4 [d]1.2
Q.35 If R1 is the input resistance and R2 is the output resistance of the voltage gain A in the common emitter configuration is
[a] α[R2/R1] [b]β [R2/R1]
[c]α [d]β
Q.36 A non conducting device is connected in a series circuit with battery and resistance. A current is found to pass through the circuit. If the polarity of the battery is reversed, the current drops to almost zero. The device may be
[a] p n junction diode
[b] an intrinsic semiconductor
[c] a p type semiconductor
[d] an n type semiconductor
Q.37 the temperature coefficient of resistance of the semiconductor is
[a] positive always [b] negative always
[c] zero [d] infinite
Q.38 in a p type semiconductor, the acceptor valence band is
[a]above the conduction band of the host crystal
[b] below the conduction band of the crystal
[c] above the valence band of the crystal
[d] below the valence band of the crystal
Q.39 The forbidden energy gap in an insular is
[a] > 6eV [b] < 6eV
[c]1 eV [d]4 eV
Q.40 In common base transistor amplifier, the phase difference between output voltage and input voltage is
[a] zero [b]1800
[c] 900 [d] 450
Q.41 Transistors may not replace vacuum tubes in all uses because
[a] because transistors requires long warm ups than the vacuum tubes
[b] vacuum tubes are more resistant in shocks and vibrations than transistors
[c] vacuum tubes can handle greater power than transistors
[d] transistors use high voltages
Q.42 The base is made thin and lightly doped because
[a] about 95% of the charge carriers may cross
[b] about 100% of the charge carriers may cross
[c] the transistors can be saved from large currents
[d] none of these
Q.43 The current gain of common base npn transistor is 0.96. what is the current gain if it is used as common emitter amplifier?
[a]16 [b] 24
[c] 20 [d] 32
Q.44 In forward biased pn junction diode, the collector current is of the order of
[a] microampere [b] milliampere
[c] ampere [d] nanoampere
Q.45 The temperature coefficient of the resistance of semiconductors is always
[a] positive [b] negative
[c] zero [d] infinite
Q.40 In an insulator, the number of electrons in the valence shell in general is
[a] less than 4 [b] more than 4
[c] equal to 4 [d] none of these
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